Various devices have been developed heretofore to measure the content of dissolved gases such as hydrogen in molten metals such as molten aluminum or molten steel. An early device is described in U.S. Pat. No. 2,861,450 issued to Ransley et al. The device shown therein referred to as the Telegas device. This device included in immersion head of generally a bell-shaped configuration and entailed discharging or debouching a carrier gas into the molten metal and recapturing bubbles using the bell-shaped device. The nitrogen reached an equilibrium with the dissolved hydrogen, which thus enabled monitoring and measurement of the dissolved hydrogen content in the metal.
An improved measurement system is described in Marten et al., U.S. Pat. No. 4,907,440, assigned to Alcan International, Ltd. In that patent, a probe is disclosed whose sensor is formed from a block of gas permeable, liquid metal-impervious material such as alumina. A carrier gas is caused to flow within the block. The block enabled entrainment of dissolved gases which diffused to the interior of the block from the ambient molten metal. The device, thus, no longer required discharge of gas bubbles into the metal nor recapturing of such bubbles.